Phenethyl-thiourea compounds and use

ABSTRACT

Novel phenylethyl-thiourea (PHET) compounds as inhibitors of reverse transcriptase and effective agents for the treatment of HIV infection, including mutant, drug-sensitive, drug-resistant, and multi-drug resistant strains of HIV.

FIELD OF THE INVENTION

The invention relates to inhibitors of reverse transcriptase effective against HIV, including mutant strains of HIV, and effective in the treatment of multi-drug resistant HIV infection.

BACKGROUND OF THE INVENTION

Agents currently used to treat HIV infection attempt to block replication of the HIV virus by blocking HIV reverse transcriptase or by blocking HIV protease. Three categories of anti-retroviral agents in clinical use are nucleoside analogs (such as AZT), protease inhibitors (such as nelfinavir), and the recently introduced non-nucleoside reverse transcriptase inhibitors (NNI), such as nevirapine.

The recent development of potent combination anti-retroviral regimens has significantly improved prognosis for persons with HIV and AIDS. Combination therapies may be a significant factor in the dramatic decrease in deaths from AIDS (decrease in death rate as well as absolute number). The most commonly used combinations include two nucleoside analogs with or without a protease inhibitor.

Nevirapine is currently the only NNI compound which has been used in combination with AZT and/or protease inhibitors for the treatment of HIV. A new series of effective drug cocktails will most likely involve other NNIs in combination with nucleoside and protease inhibitors as a triple action treatment to combat the growing problem of drug resistance encountered in single drug treatment strategies.

The high replication rate of the virus unfortunately leads to genetic variants (mutants), especially when selective pressure is introduced in the form of drug treatment. These mutants are resistant to the anti-viral agents previously administered to the patient. Switching agents or using combination therapies may decrease or delay resistance, but because viral replication is not completely suppressed in single drug treatment or even with a two drug combination, drug-resistant viral strains ultimately emerge. Triple drug combinations employing one (or two) nucleoside analogs and two (or one) NNI targeting RT provide a very promising therapy to overcome the drug resistance problem. RT mutant strains resistant to such a triple action drug combination would most likely not be able to function.

Dozens of mutant strains have been characterized as resistant to NNI compounds, including L1001, K103N, V106A, E138K, Y118C and Y188H. In particular, the Y181C and K103N mutants may be the most difficult to treat, because they are resistant to most of the NNI compounds that have been examined.

Recently, a proposed strategy using a knock-out concentration of NNI demonstrated very promising results. The key idea in this strategy is to administer a high concentration of NNI in the very beginning stages of treatment to reduce the virus to undetectable levels in order to prevent the emergence of drug-resistant strains. The ideal NNI compound for optimal use in this strategy and in a triple action combination must meet three criteria:

1) very low cytotoxicity so it can be applied in high doses;

2) very high potency so it can completely shut down viral replication machinery before the virus has time to develop resistant mutant strains; and

3) robust anti-viral activity against current clinically observed drug resistant mutant strains.

Novel NNI designs able to reduce RT inhibition to subnanomolar concentrations with improved robustness against the most commonly observed mutants and preferably able to inhibit the most troublesome mutants are urgently needed. New antiviral drugs will ideally have the following desired characteristics: (1) potent inhibition of RT; (2) minimum cytotoxicity; and (3) improved ability to inhibit known, drug resistant strains of HIV. Currently, few anti-HIV agents possess all of these desired properties.

Two non-nucleoside inhibitors (NNI) of HIV RT that have been approved by the U.S. Food and Drug Administration for licensing and sale in the United States are nevirapine (dipyridodiazepinone derivative) and delavirdine (bis(heteroaryl)piperazine (BHAP) derivative, BHAP U-90152). Other promising new non-nucleoside inhibitors (NNIs) that have been developed to inhibit HIV RT include dihydroalkoxybenzyloxopyrimidine (DABO) derivatives, 1-[(2-hydroxyethoxy)methyl]-6-(phenylthio)thymine (HEPT) derivatives, PHETrahydrobenzondiazepine (TIBO), 2′, 5′-Bis-O-(tert-butyldimethylsilyl)-3′-spiro-5″-(4″-amino-1″,2″-oxathiole-2″,2′-dioxide)pyrimidine (TSAO), oxathiin carboxanilide derivatives, quinoxaline derivatives, thiadiazole derivatives, and phenethylthiazolylthiourea (PETT) derivatives.

NNIs have been found to bind to a specific allosteric site of HIV- RT near the polymerase site and interfere with reverse transcription by altering either the conformation or mobility of RT, thereby leading to a noncompetitive inhibition of the enzyme (Kohlstaedt, L. A. et al., Science, 1992, 256, 1783-1790).

A number of crystal structures of RT complexed with NNIs have been reported (including α-APA, TIBO, Nevirapine, and HEPT derivatives), and such structural information provides the basis for further derivatization of NNI aimed at maximizing binding affinity to RT. However, the number of available crystal structures of RT NNI complexes is limited.

Given the lack of structural information, alternate design procedures must be relied upon for preparing active inhibitors such as PETT and DABO derivatives. One of the first reported strategies for systematic synthesis of PETT derivatives was the analysis of structure-activity relationships independent of the structural properties of RT and led to the development of some PETT derivatives with significant anti-HIV activity (Bell, F. W. et al., J. Med. Chem., 1995, 38, 4929-4936; Cantrell, A. S. et al., J. Med. Chem., 1996, 39, 4261-4274).

A series of selected phenethylthiazolylthiourea (PETT) derivatives targeting the NNI binding site of HIV reverse transcriptase (RT) were synthesized and tested for anti-human immunodeficiency virus (HIV) activity. The structure based design and synthesis of these PETT derivatives were aided by biological assays and their anti-HIV activity. Some of these novel derivatives were more active than AZT or Troviridine and abrogated HIV replication at nanomolar concentrations without any evidence of cytotoxicity. These compounds are useful in the treatment of HIV infection, and have particular efficacy against mutant strains, making them useful in the treatment of multi-drug resistant HIV.

SUMMARY OF THE INVENTION

The invention provides phenethyl-thiourea (PHET) compounds as non-nucleoside inhibitors (NNI) of HIV reverse transcriptase, and particularly methyl-phenethyl-thiourea compounds as particularly potent inhibitors. The PHET compounds, compositions, and methods of the invention are useful in the treatment of HIV infection, with particular efficacy against multiple strains of HIV, including multi-drug resistant mutant strains.

The PHET compounds, compositions, and methods of the invention are useful for inhibiting reverse transcriptase activity and inhibiting replication of multiple strains of HIV, including therapy-naive, drug-resistant, and multi-drug resistant mutant strains. In particular, the PHET compounds of the invention are useful for treating retroviral infection in a subject, such as an HIV-1 infection, by administration of the PHET compounds of the invention, for example, in a pharmaceutical composition.

The PHET compounds of the invention contain a phenyl ring as shown in Formula I. The phenyl ring is preferably substituted (R_(n)) with an electron-donating group at the para position, such as methyl or methoxy. An exemplary, and particulary preferred PHET compound of the invention is HI-244, having the structure shown in Formula II.

The PHET compounds and compositions useful in the invention exhibit:

1. very low cytotoxicity;

2. very high potency; and

3. potent activity against at least one clinically observed drug resistant mutant strain.

Specific compounds and methods of the invention are described more fully in the Detailed Description and in the Examples below.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A is a composite binding pocket of the NNI binding site of HIV-1 RT illustrated as grid lines representing the collective van der Waals surface; a stick model of the docked compound HI-244 is shown; and

FIG. 1B is a Connolly surface representation of HI-244 in the NNI binding site; residues in contact with the compound are labeled and shown in the stick model.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

When used herein, the following terms have the indicated meanings:

“NNI” means non-nucleoside inhibitor. In the context of the invention, non-nucleoside inhibitors of HIV reverse transcriptase (RT) are defined.

“Mutant HIV” means a strain of HIV having one or more mutated or altered amino acids as compared with wild type.

“Multi-Drug Resistant HIV” means one or more HIV strain which is resistant to treatment with one or more chemotherapeutic agent.

“Therapeutically effective amount” is a dose which provides some therapeutic benefit on administration, including, in the context of the invention, reduced viral activity or viral load in a patient, and also including inhibition of viral RT activity and/or replication of virus.

Compounds of the Present Invention

Compounds of the present invention are phenethyl-thiourea (PHET) compounds useful as non-nucleoside inhibitors of RT having the formula I:

The phenyl ring may be substituted or unsubstituted (R_(n)), and is preferably substituted with an electron donating group, most preferably at the para position. For example, R can be H, methyl, methoxy, halo, and the like, and most preferably is methyl. The value of n can be 0 to 6, and preferably is 1.

R₁ is a cyclic moiety, which may be substituted or not (X), such as phenyl, pyridyl, piperidinyl, piperonyl, morphorlyl, ftiryl, and the like, and can be, for example, cyclo(C₃-C₁₂) alkyl, cyclo(C₃-C₁₂) alkenyl, isothiazolyl, tetrazolyl, triazolyl, pyridyl, imidazolyl, phenyl, napthyl, benzoxazolyl, benzimidazolyl, thiazolyl, oxazolyl, benzothiazolyl, pyrazinyl, pyridazinyl, thiadiazolyl, benzotriazolyl, pyrolyl, indolyl, benzothienyl, thienyl, benzofuryl, quinolyl, isoquinolyl, pyrazolyl, and the like.

In one preferred embodiment, R₁ is pyridyl, optionally substituted (X) with one or more substituents, for example, with an alkyl, alkoxy, halo, or hydroxy group. More preferably, R₁ is pyridyl substituted with a halogen such as bromine or chlorine. An exemplary compound of the invention is N-[2-(4-methylphenethyl)]-N′-[2-(5-bromopyridyl)]-thiourea (HI-244).

The compounds of the invention preferably bind to a specific allosteric site of HIV-RT near the polymerase site and interfere with reverse transcription, for example, by altering either the conformation or mobility of RT.

Acid Salts

The compounds of the invention may also be in the form of pharmaceutically acceptable acid addition salts. Pharmaceutically acceptable acid addition salts are formed with organic and inorganic acids.

Examples of suitable acids for salt formation are hydrochloric, sulfuric, phosphoric, acetic, citric, oxalic, malonic, salicylic, malic, gluconic, fumaric, succinic, asorbic, maleic, methanesulfonic, and the like. The salts are prepared by contacting the free base form with a sufficient amount of the desired acid to produce either a mono or di, etc. salt in the conventional manner. The free base forms may be regenerated by treating the salt form with a base. For example, dilute solutions of aqueous base may be utilized. Dilute aqueous sodium hydroxide, potassium carbonate, ammonia, and sodium bicarbonate solutions are suitable for this purpose. The free base forms differ from their respective salt forms somewhat in certain physical properties such as solubility in polar solvents, but the salts are otherwise equivalent to their respective free base forms for purposes of the invention. Use of excess base where R is hydrogen gives the corresponding basic salt.

Methods of Using the Compounds of the Invention

The compounds of the invention are useful in methods for inhibiting reverse transcriptase activity of a retrovirus. Retroviral reverse transcriptase is inhibited by contacting RT in vitro or in vivo, with an effective inhibitory amount of a compound of the invention. The compounds of the invention also inhibit replication of retrovirus, particularly of HIV, such as HIV-1. Viral replication is inhibited, for example, by contacting the virus with an effective inhibitory amount of a compound of the invention.

The methods of the invention are useful for inhibiting reverse transcriptase and/or replication of multiple strains of HIV, including mutant strains, and include treating a retroviral infection in a subject, such as an HIV-1 infection, by administering an effective inhibitory amount of a compound or a pharmaceutically acceptable acid addition salt of a compound of the Formula I. The compound or inhibitor of Formula I is preferably administered in combination with a pharmaceutically acceptable carrier, and may be combined with specific delivery agents, including targeting antibodies and/or cytokines. The compound or inhibitor of the invention may be administered in combination with other antiviral agents, immunomodulators, antibiotics or vaccines.

The compounds of Formula I can be administered orally, parentally (including subcutaneous injection, intravenous, intramuscular, intrastemal or infusion techniques), by inhalation spray, topically, by absorption through a mucous membrane, or rectally, in dosage unit formulations containing conventional non-toxic pharmaceutically acceptable carriers, adjuvants or vehicles. Pharmaceutical compositions of the invention can be in the form of suspensions or tablets suitable for oral administration, nasal sprays, creams, sterile injectable preparations, such as sterile injectable aqueous or oleagenous suspensions or suppositories. In one embodiment, the PHET compounds of the invention can be applied intravaginally and/or topically, for example in gel form, for prevention of heterosexual transmission of HIV.

For oral administration as a suspension, the compositions can be prepared according to techniques well-known in the art of pharmaceutical formulation. The compositions can contain microcrystalline cellulose for imparting bulk, alginic acid or sodium alginate as a suspending agent, methylcellulose as a viscosity enhancer, and sweeteners or flavoring agents. As immediate release tablets, the compositions can contain microcrystalline cellulose, starch, magnesium stearate and lactose or other excipients, binders, extenders, disintegrants, diluents and lubricants known in the art.

For administration by inhalation or aerosol, the compositions can be prepared according to techniques well-known in the art of pharmaceutical formulation. The compositions can be prepared as solutions in saline, using benzyl alcohol or other suitable preservatives, absorption promoters to enhance bioavailability, fluorocarbons or other solubilizing or dispersing agents known in the art.

For administration as injectable solutions or suspensions, the compositions can be formulated according to techniques well-known in the art, using suitable dispersing or wetting and suspending agents, such as sterile oils, including synthetic mono- or diglycerides, and fatty acids, including oleic acid.

For rectal administration as suppositories, the compositions can be prepared by mixing with a suitable non-irritating excipient, such as cocoa butter, synthetic glyceride esters or polyethylene glycols, which are solid at ambient temperatures, but liquefy or dissolve in the rectal cavity to release the drug.

Dosage levels of approximately 0.02 to approximately 10.0 grams of a compound of the invention per day are useful in the treatment or prevention of retroviral infection, such as HIV infection, AIDS or AIDS-related complex (ARC), with oral doses 2 to 5 times higher. For example, HIV infection can be treated by administration of from about 0.1 to about 100 milligrams of compound per kilogram of body weight from one to four times per day. In one embodiment, dosages of about 100 to about 400 milligrams of compound are administered orally every six hours to a subject. The specific dosage level and frequency for any particular subject will be varied and will depend upon a variety of factors, including the activity of the specific compound the metabolic stability and length of action of that compound, the age, body weight, general health, sex, and diet of the subject, mode of administration, rate of excretion, drug combination, and severity of the particular condition.

The compound of Formula I can be administered in combination with other agents useful in the treatment of HIV infection, AIDS or ARC. For example, the compound of the invention can be administered in combination with effective amounts of an antiviral, immunomodulator, anti-infective, or vaccine. The compound of the invention can be administered prior to, during, or after a period of actual or potential exposure to retrovirus, such as HIV. ps Methods of Making the Compounds of the Invention

The compounds of the invention may be prepared as shown in Schemes 1 and 2. In general, an appropriate phenethylamine or pyridylethylamine (R₁-NH₂) is reacted with 1,1 ′-thiocarbonyl-diimidazole in acetonitrile solvent at ambient temperature for approximately 12 hours to form a thiocarbonyl reagent. The reaction product is then condensed with a substituted or non-substituted phenylamine in an aprotic solvent such as dimethyl-formamide (DMF) at elevated temperature, such a 100° C., for an extended period of time such as about 15 hours. The desired PHET compound is purified by column chromatography.

The PHET compounds of the invention can be synthesized as described above, or by other, known synthetic methods.

EXAMPLES

The invention may be further clarified by reference to the following Examples, which serve to exemplify the embodiments, and not to limit the invention in any way.

Example 1 Synthesis and Characterization of Thiourea Inhibitors

In the present study, we replaced the pyridyl ring of trovirdine with a substituted or unsubstituted phenyl group that fits well with the Wing 2 region of the NNI binding pocket. The PHET compounds were synthesized as shown in Scheme 1, in which a thiocarbonyl reagent was prepared from phenethylamine or pyridylethylamine and 1,1′-thiocarbonyl-diimidazole in acetonitrile solvent at room temperature for 12 hours, and condensed with the appropriate 2-phenyl amino compounds in dimethyl formamide (DMF) at 100° C. for 15 hours. After work up, the derivatives were purified by column chromatography. Trovirdine, a comparative standard, was synthesized according to the method described in Bell et.al., 1995, J. Med. Chem 38:4929.

Characterization of Synthesized Compounds:

Proton and carbon nuclear magnetic resonance spectra were recorded on a Varian spectrometer using an automatic broad band probe. Unless otherwise noted, all NMR spectra were recorded in CDCl₃ at room temperature. The chemical shifts reported are in parts per million relative to tetramethyl silane as standard. The multiplicity of the signals were designated as follows: s, d, dd, t, q, m which corresponds to singlet, doublet, doublet of doublet, triplet, quartet and multiplet respectively. UV spectra were recorded from a Beckmann Model #DU 7400 UV/Vis spectrometer using a cell path length of 1 cm. Fourier Transform Infra Red spectra were recorded using an FT-Nicolet model Protege #460 instrument. The infra red spectra of the liquid samples were run as neat liquids using KBr discs. Mass spectrum analysis was conducted using either a Finnigan MAT 95 instrument or a Hewlett-Packard Matrix Assisted Laser Desorption (MALDI) spectrometer model #G2025A .The matrix used in the latter case was cyano hydoxy cinnamic acid. Melting points were determined using a Melt John's apparatus and uncorrected. Elemental analysis were was performed by Atlantic Microlabs (Norcross, Ga.). Column chromatography was performed using silica gel obtained from the Baker Company. The solvents used for elution varied depending on the compound and included one of the following: ethyl acetate, methanol, chloroform, hexane, methylene chloride and ether. Characterizataion data for the synthesized compounds is shown below:

N-[2-(4-methoxyphenethyl)]-N′-[2-(5-bromopyridyl)]thiourea (HI-238) yield: 85%, mp.178-179° C.; UV:(MeOH) λmax: 205, 226, 275, 305 nm; IR(KBr) ν 3221, 3159, 3042, 2931, 2827, 1587, 1510, 1464, 1311, 1225, 1165, 1088, 1034, 820, 773, 708 cm⁻; ¹HNMR (CDCl₃) δ 11.30 (bs, 1H),7.87 (bs, 1H), 8.00-7.99 (d, 1H), 7.21-7.18 (dd, 1H), 6.95-6.92 (d, 2H),6.88-6.85(d, 2H), 4.00-3.93 (q, 2H), 3.81 (s, 3H), 2.96-2.92(t, 2H); ¹³C(CDCl₃) δ 178.1, 158.0, 151.9, 145.8, 140.7, 130.6, 128.6, 113.8, 113.7, 112.1, 55.1, 46.9 and 33.8; Maldi Tof mass: 366 (M+1), Calculated mass: 365; Anal. (C₁₅H₁₆BrN₃OS) C, H, N, S;

N-[2-(4-fluorophenethyl)]-N′-[2-(5-bromopyridyl)]thiourea (HI-242) yield: 69%; mp 177-178° C.; UV:(MeOH) λmax: 208, 211, 274, 306 nm, IR(KBr)ν 3456, 3213, 3155, 3086, 3028, 2868, 1595, 1560, 1533, 1477, 1336, 1308, 1238, 1211, 1173, 1136, 1092, 1026, 933, 869, 827, 791, 741, 694 cm⁻¹; ¹HNMR (CDCl₃) δ 11.29 (bs, 1H),9.27 (bs, 1H), 8.04-8.03 (dd,1H), 7.73-7.69(dd,1H), 7.271-7.22(m, 1H), 7.04-6.99 (m,3H), 6.83-6.79 (d, 1H), 4.03-3.96 (q, 2H), 3.02-2.97 (t, 2H); ¹³C(CDCl₃) δ0 179.1, 163.2, 151.6, 146.3, 141.2, 134.3, 130.3, 130.2, 115.2, 113.5, 112.8, 47.0 and 34.1; ¹⁹F(CDCl₃) δ-40.55 (m), Maldi Tof mass: 354.8 (M+1), Calculated mass: 354; Anal. (C₁₄H₁₃BrFN₃S) C, H, N,S;

N-[2-(4-bromophenethyl)]-N′-[2-(5-bromopyridyl)]thiourea (HI-243) yield: 75%; mp 184-185° C.; UV (MeOH) λmax: 207, 257, 276, 306 nm, IR(KBr) ν 3454, 3221, 3153, 3086, 3022, 2929, 1595, 1560, 1531, 1471, 1402, 1338, 1304, 1227, 1169, 1091, 1072, 1013, 820, 708 cm⁻¹; ¹HNMR (CDCl₃) δ 11.28 (bs, 1H), 9.21 (bs, 1H), 8.04-8.03 (dd,1H), 7.46-7.43(dd, 2H), 7.18-7.14 (m, 2H), 6.81-6.78 (d, 2H), 4.03-3.96 (q, 2H), 3.00-2.96 (t, 2H), ¹³C(CDCl₃) δ 179.2, 151.6, 146.3, 141.3, 133.6, 131.6, 130.6, 113.5, 112.9, 46.7 and 34.3; Maldi Tof mass: 416 (M+1), Calculated mass : 415; Anal. (C₁₄H₁₃Br₂ N₃S) C, H, N,S, Br;

N-[2-(4-methylphenethyl)]-N′-[2-(5-bromopyridyl)]thiourea (HI-244) yield: 62%; mp. 159-162° C.; UV (MeOH) λmax 212, 275, 305 nm; IR (KBr) ν 3439, 3228, 3161, 3086, 2917, 2866, 1595, 1543, 1466, 1307, 1265, 1229, 1188, 1140, 1003, 829, 812, 777 cm⁻¹; ¹HNMR (CDCl₃) δ 11.27 (bs, 1H),9.07 (bs, 1H), 8.01-8.00(s, 1H), 7.71-7.67 (d, 1H), 7.19-7.12 (m, 4H), 6.78-6.75 (d, 1H), 4.03-3.97 (q, 2), 2.99-2.95 (t, 2H),2.36 (s, 3H); ¹³C(CDCl₃) δ 178.9, 151.6, 146.4, 141.1, 136.1, 135.5, 129.2, 128.7, 113.4, 112.7, 47.2, 34.4 and 21.1; Maldi Tof mass: 351 (M+1), Calculated mass: 350; Anal. (C₁₅H₁₆Br N₃S) C, H, N, S;

N-[2-(4-chlorophenethyl)]-N′-[2-(5-bromopyridyl)]thiourea (HI-255) yield: 71%; mp.180-183° C.; UV (MeOH) λmax206, 209, 219,256, 275, 305 nm; IR(KBr) ν 3221, 3153, 3086, 3022, 2931, 1674, 1593, 1562, 1533, 1473, 1406, 1340, 1304, 1265, 1227, 1169, 1138, 1092, 1016, 820, 752, 714 cm⁻¹; ¹HNMR (CDCl₃) δ 11.40 (bs, 1H),9.34 (bs, 1H), 8.15-8.14(s, 1H), 7.84-7.80 (d, 1H), 7.42-7.40 (m, 2H), 7.40-7.33 (m, 2H), 7.33-7.30 (m, 1H), 6.92-6.89 (d, 1H), 4.10-4.07 (q, 2H), 3.13-3.08 (t, 2H); ¹³C(CDCl₃) δ 179.2, 151.6, 146.3, 141.3, 137.1, 130.2,128.6,113.5, 112.8, 46.8 and 34.2; Maldi Tof mass: 372 (M+1), Calculated mass: 371.0; Anal. (C₁₄H₁₃BrClN₃S) C, H, N, S;

N-[2-(5-Bromopyridinyl)]-N′-[2-(Phenethyl)]thiourea (HI-275) mp: 162-163° C.; UV(MeOH) λ_(max): 207, 276, 306 nm; IR(KBr) ν 3216, 3160, 3083, 3025, 2925, 2861, 1592, 1552, 1529, 1475, 1357, 1311, 1226, 1166, 1091, 1070, 1002, 864, 823, 746, 698, 561, 511 cm⁻¹; ¹HNMR (CDCl₃) δ 11.31 (bs, 1H), 9.42 (bs, 1H), 7.99-7.98 (d, 1H), 7.70-7.66 (dd, 1H), 7.37-7.26 (m, 5H), 6.84-6.81 (d, 1H), 4.06-4.00 (q, 2H), 3.04-2.99 (t, 2H); ¹³C NMR (CDCl₃) δ 179.0, 151.7, 146.2, 141.1, 138.6, 128.8, 128.5, 126.6, 113.5, 112.7, 47.0, 34.8;

N-[2-(4-hydroxyphenethyl)]-N′-[2-(5-bromopyridyl)]thiourea (HI-256) yield: 71%; mp 159-162° C.; UV (MeOH) λmax 205, 208, 274, 305 nm; IR (KBr)ν 3224, 3159, 3089, 3041, 2933, 2870, 1595, 1558, 1533, 1514, 1332, 1306, 1265, 1227, 1186, 1136, 1094, 1007, 910, 862, 827, 708 cm⁻¹; ¹HNMR (DMSO-d₆) δ 11.30 (bs, 1H),10.17 (bs, 1H), 8.78 (bs,1H), 8.03-8.02(s, 1H), 7.67-7.65(d, 1H), 7.11-7.09 (d,2H), 7.03-6.99(d,1H), 6.82-6.80 (d, 2H), 3.96-3.90 (q, 2H), 2.92-2.83 (t, 2H), ¹³C(CDCl₃) δ 178.9, 155.4, 151.9, 145.4, 140.3, 129.2, 128.9, 114.9,113.9,111.6, 46.7 and 33.5, Maldi Tof mass: 353 (M+1), Calculated mass: 352; Anal. (C₁₄H₁₄BrN₃OS) C, H, N, S, Br.

Example 3 Antiviral Activity of Substituted Thiourea Compounds

Purified RT Assays for Anti-HIV Activity

The synthesized compounds were tested for RT inhibitory activity (IC₅₀[rRT]) against purified recombinant HIV RT using the cell-free Quan-T-RT system (Amersham, Arlington Heights, Ill.), which utilizes the scintillation proximity assay principle as described in Bosworth, et al., 1989, Nature 341:167-168. In the assay, a DNA/RNA template is bound to SPA beads via a biotin/strepavidin linkage. The primer DNA is a 16-mer oligo(T) which has been annealed to a poly(A) template. The primer/template is bound to a strepavidin-coated SPA bead.

³H-TTP is incorporated into the primer by reverse transcription. In brief, ³H-TTP, at a final concentration of 0.5 μCi/sample, was diluted in RT assay buffer (49.5 mM Tris-Cl, pH 8.0, 80 mM KCl, 10 Mm MgCl₂, 10 mM DTT, 2.5 mM EGTA, 0.05% Nonidet-P-40), and added to annealed DNA/RNA bound to SPA beads. The compound being tested was added to the reaction mixture at 0.001 μM-100 μM concentrations. Addition of 10 mU of recombinant HIV RT and incubation at 37° C. for 1 hour resulted in the extension of the primer by incorporation of ³H-TTP. The reaction was stopped by addition of 0.2 ml of 120 mM EDTA. The samples were counted in an open window using a Beckman LS 7600 instrument and IC₅₀ values were calculated by comparing the measurements to untreated samples.

In addition, the anti-HIV activity of the compounds was measured by determining their ability to inhibit the replication of the HIV-1 strain HTLVIIIB in peripheral blood mononuclear cells (PBMC) from healthy volunteer donors, using the method described in Uckun et.al., 1998, Antimicrobial Agents and Chemotherapy 42:383. The HIV strain HTLVIIIB was kindly provided by Dr. Neal T. Wetherall, VIROMED Laboratories, Inc., and was propagated in CCRF-CEM cells.

Normal human peripheral blood mononuclear cells (PBMNC) from HIV-negative donors were cultured 72 hours in RPMI 1640 supplemented with 20% (v/v) heat-inactivated fetal bovine serum (FBS), 3% interleukin-2,2 mM L-glutairine, 25 mM HEPES, 2 μL, NAHCO, 50 mg/mL gentamicin, and 4 μg/mL phytohemagglutinin prior to exposure to HIV-1 or other HIV strain at a multiplicity of infection (MOI) of 0.1 during a one-hour adsorption period at 37° C. in a humidified 5% CO2 atmosphere. Subsequently, cells were cultured in 96-well microplates (100 μL/well; 2×10⁶ cells/mL, triplicate wells) in the presence of various inhibitor concentrations. Aliquots of culture supernatants were removed from the wells on the 7^(th) day after infection for p24 antigen p24 enzyme immunoassays (EIA), as previously described in Erice et al., 1993, Antimicrob. Ag. Chemotherapy 37:385-838. The applied p24 EIA was the unmodified kinetic assay commercially available from Coulter Corporation/Immunotech, Inc. (Westbrook, Me.). Percent inhibition of viral replication was calculated by comparing the p24 values from the test substance-treated infected cells with p24 values from untreated infected cells (i.e, virus controls).

A Microculture tetrazolium Assay (MTA), using 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino)-carbonyl]-2H-PHETrazolium hydroxide (XTT), was performed to evaluate the cytotoxicity of the compounds, using the methods described, for example, in Uckun et.al., 1998, Antimicrobial Agents and Chemotherapy 42:383; and Mao et.al., 1998, Bioorg. Med. Chem. Lett. 8:2213.

Data are presented in Table 1 as the IC₅₀ values for inhibition of HIV p24 antigen production in PBMC (concentration at which the compound inhibits p24 production by 50%).

TABLE 1

IC₅₀ IC₅₀ IC₅₀ IC₅₀ RT-MDR A17 rRT HTLV _(m)B (Y106A) (Y181C) CC₅₀ Compound R₁ (μM) (μM) (μM) (μM) (μM) 1. Trovirdine Pyridyl 0.8 0.007 0.02 0.5 >100 2. HI-275 Phenyl 1.3 N.D. N.D. N.D. N.D. 3. HI-238 4-methoxyphenyl 0.9 0.015 N.D. N.D. >100 4. HI-242 4-flurophenyl 6.4 N.D. N.D. N.D. N.D. 5. HI-255 4-chlorophenyl 2.5 20.8 N.D. N.D. N.D. 6. HI-243 4-bromophenyl 0.9 0.07 >0.001 1.0 >100 7. HI-231 4-nitrophenyl >100 N.D. N.D. N.D. N.D. 8. HI-244 4-methylphenyl 0.1 0.007 >0.001 0.07  71 9. HI-256 4-hydroxyphenyl 87.7 3.067 N.D. N.D. >100

These data demonstrate the surprisingly potent antiviral activity of mono-substituted phenethyl thiourea compounds, particularly substituted with an electron donating group at the para position of the phenyl ring. The ability of HI-244 to inhibit HIV-1 replication, including resistant strains, in human PBMC was also evaluated using the methods described above. HI-244 effectively inhibited replication of the HIV-1 strain HTLV_(IIIB) in PBMC with an IC₅₀ value of 0.007 μM, which is equal ot the IC₅₀ value of trovirdine (Table 1).

HI-244 was 20-times more effective than trovirdine against the multidrug resistant HIV-1 strain RT-MDR with a V106A mutation (as well as additional mutations involving the RT residues 74V, 41L, and 215Y) and 7-times more potent than trovirdine against the NNI-resistant HIV-1 strain A17 with a Y181C mutation. HI-244 was not cytotoxic to PBMC even at a 100 μM concentration. Thus, the selectivity index for HI-244 was:

>10,000 against the wild-type HIV-1 strain HTLV_(IIIB),

>71,000 against the multidrug-resistant V106A mutant strain RT-MDR, and

>1,000 against the NNI-resistant Y181C mutant strain A17.

These findings establish the lead para-methyl substituted phenyl thiourea compound HI-244 as an effective NNI against drug-sensitive, NNI-resistant, and multidrug-resistant strains of HIV-1.

As described in our prior publications, the para-substituted group lies within a hydrophobic region indicated by the composite NNI binding pocket (FIG. 1A). See for example, Vig et al., 1998, Bioorg. Med. Chem, 6:1789; and Sudbeck et al., 1998, Antimicro. Agents Chemother., 1998,_(—):3225-33. This region contains the aromatic rings of residues W229 and Y188 which would interact favorably with a hydrophobic group (FIG. 1B). Therefore, the observed inhibition level of the para-substituted compounds against the wild-type HIV-1 is generally proportional to the hydrophobicity of the para-substituted group (Table 2). The potency of the para-substitued compounds is consistent with the following trend: hydrophobic group>polar group>hydrophilic group.

The para-methyl group on the HI-244 compound is predicted to reside closer to the Y181 residue (C-to Cα distance+5.5 Å) than to the V106 residue (C-to-Cα distance+8.1 A). Therefore, the Y181 mutation would have reduced the potency of a para-substituted compound more than the V106 mutation would. This reasoning is consistent with the observation that the Y181C mutant strain (A 17 strain) has 10-fold resistance to HI-244 whereas the V106A mutant strain (RT-MDR) shows no resistance, and in fact shows improved activity.

TABLE 2 K_(i) ^(c) IC₅₀ IC₅₀ MS LIPO (calc.) rRT* p24 Compounds R₁ (Å)^(a) BS(%)^(b) score (μM) (μM) (μM) 1. Trovirdine Pyridyl 276 84 679 0.7 0.8 0.007 2. HI-275 Phenyl 274 84 672 0.8 1.3 ND 3. HI-238 4-methoxyphenyl 302 84 729 1.2 0.9 0.015 4. HI-242 4-flurophenyl 284 81 674 7.8 6.4 ND 5. HI-255 4-chlorophenyl 293 81 696 4.7 2.5 ND 6. HI-243 4-bromophenyl 295 82 708 6.3 0.9 0.07  7. HI-231 4-nitrophenyl 301 79 695 84 >100 ND 8. HI-244 4-methylphenyl 294 84 724 0.25 0.1 0.007 9. HI-256 4-hydroxyphenyl 286 82 686 104 87.7 ND *rRT is recombinant HIV reverse transcriptase ^(a)MS is the molecular surface area calculated by Commonny“s MS program ^(b)BS is burried surface, or % of the molecular surface in contact with protein calculated by Ludi based on docked positions. ^(c)Ludi K_(i) values were calculated based on modified empirical score function in Ludi program. ND is not determined, for compounds with IC₅₀[rRT] greater than 1.0

The apparent van der Waals contact between the compound and tyrosine residue 181 after its mutation to a smaller cystein residue may help explain the observed resistance. However, we are not certain about the reason for the demonstrated superior activity of HI-244 against the V106A RT mutant relative to the wild-type RT. The V106A mutation may enable the compound to reposition itself in the binding site, leading to improved contacts between thepara-methyl group and Y188 resulting in a better binding affinity. In contrast, trovirdine would not benefit from such a mutation due to the absence of apara-methyl group (trovirdine is 20 times less potent than HI-244 against the RT-MDR strain).

With respect to trovirdine, the addition of aparamehtyl group in HI-244 increases the molecular volume in the Wing 2 region of the binding site by 18 Å³. In the NNI-resistant A17 strain (Y181C mutation), the Wing 2 region of the mutant becomes larger when Y181 is mutated to a smaller cystein residue, as observed in the crystal structure of the Y181C mutant. These results showing a 7-fold higher potency of HI-244 relative to trovirdine are consistent with our previously reported hypothesis that an NNI compound containing larger (and compatible) functional groups at the Wing 2 region of the binding site can provide better inhibitor activity against these HIV RT mutants.

All publications, patents, and patent documents described herein are incorporated by reference as if fully set forth. The invention described herein may be modified to include alternative embodiments. All such obvious alternatives are within the spirit and scope of the invention, as claimed below. 

We claim:
 1. A method for treating multi-drug resistant NNI resistant, and therapy naïve HIV infection in a subject comprising administering to said subject an anti-HIV effcctive amount of a compound of formula I:

wherein: n is 0 to 5; each R is an elecron donating group; and R₁ is substituted or urnsubstituted pyridyl.
 2. The method of claim 1, wherein R₁ is substituted with H, methyl, methoxy, or halo.
 3. The method of claim 1, wherein n is
 1. 4. The method of claim 1, wherein R is methyl or methoxy.
 5. The method of claim 1, wherein R₁ is pyridyl.
 6. The method of claim 1, wherein R₁ is 5-bromo-pyridyl.
 7. The method of claim 1, wherein R is para-methyl.
 8. The method of claim 1, wherein R is para-methoxy.
 9. A method for inhibiting replication of multi-drug resistait, NNI resistant, and therapy naïve HIV comprising contacting said HIV with an inhibitory amount of a compound of formula I:

wherein: n is 0 to 5; each R is an electron donating group; and R₁ is substituted or unsubstituted pyridyl.
 10. The method of claim 9, wherein R₁ is substituted with H, methyl, methoxy, or halo.
 11. A method for inhibiting multi-drug resistant, NNI resistant, and therapy naïve HIV reverse transcriptase comprisig contacting said HIV reverse transcriptase with an effective inhibitory amount of a compound of formula I:

wherein: n is 0 to 5; each R is an electron donating group; and R₁ is substituted or unsubstitated pyridyl.
 12. The method of claim 11, wherein R₁ is substituted with H, methyl, methoxy, or halo.
 13. The method of any of claims 1, 8, or 9, wherein the compound is: [2-(4-methoxyphenethyl)]-N′-[2-(5-bromopyridyl)]thiourea (HI-238); or N-[2-(4-methylphenethyl)]-N′-[2-(5-bromopyridyl)]thiourea (HI-244). 